Re: Question about the GdkGC

[Tristan Van Berkom <vantr touchtunes com>]

Tom Liu wrote:

> Ok I understand why create GdkGC and use GdkGC both need the GdkDrawable
> parameter because one created GC can apply to multiple window.
>
> But how about the performance?
> I saw a program need to draw 10 color on a drawable. They just create 10
> GC! And they nevery release these GC.
> It this right way to do so? Should I create one GC and change the colors
> when need it?
>
> I am a windows programmer, usually when I need to draw something in the
> window, I just get a gc, change color, draw, change color back, release
> gc.
>
> Looks gtk work like this. 
> 	Create multiple GC, use these when needed over and over again.
>  
This is a question about load balancing and resource consumtion; I 
really suggest
that the application developer (you) consider the context of the application
before deciding what is the optimal proceedure.

If you rarely ever need to draw; you might want to <allocate-setup 
colours-draw-release>
If you want to maintain a framerate; you might want to have multiple 
GC's ready and just <draw>
You might also come to the conclusion that in your application; having a 
few GC's always present
is a negligable amount of memory to "waste" and do it what ever way is 
fastest to develop ;-)

Regards,
                               -Tristan

> -----Original Message-----
> From: gtk-app-devel-list-admin gnome org
> [mailto:gtk-app-devel-list-admin gnome org] On Behalf Of Tristan Van
> Berkom
> Sent: Wednesday, November 12, 2003 11:56 AM
> To: Tom Liu
> Cc: gtk-app-devel-list gnome org
> Subject: Re: Question about the GdkGC
>
> Tom Liu wrote:
>
>  
>
> > When I create a GdkGC, I have to give a GdkDrawable to attach this GC,
> > But when I draw line or rectangle, I still need the GdkDrawable as
> > parameter.
> >
> >    
> You need to provide a GdkDrawable so that the GdkGC can reference a
> colormap; the colormap is created when you create a GdkDrawable
> and; if I'm not mistaken; thats because creating the colormap requires
> some knowlage of the rendering architechture (Win or XFree86)
> (and thats handled at the GdkDrawable level).
>
>  
>
> > Is these because one GdkGC can work on multile GdkDrawable after it
> > created?
> >
> >
> >    
> Yes it can.
>
>  
>
> > Another question: the CreateGC and releaseGC is a expensive job? Should
> > I create and release it every time I need to draw or just keep a global
> > copy for better performance.
> >
> >
> >    
> A GdkGC is like a structure that holds a bunch of paramaters
> to draw with when using any GdkDrawables; instead of passing
> alot of arguments to the drawing functions; the arguments that
> probably won't change from one function call to the next; are
> stored in the graphics context.
>
> Does that help ?
>
> Regards,
>                                                -Tristan
>
>